Calculating inductance, Datasheet says AsubL =75 (nH)

A

amdx

Guest
I know and use the formulas for calculating turns on a core.
For Ferrite cores
N=1000 x sqrt of (your desired L (in mH) / AsubL (mH/1000turns)
For Iron Cores
N=100 x sqrt of (your desired L (in uH) / AsubL (uH/100)

Now I have a core that says AsubL is 75 (nH)
Assuming that is 75nH for one turn, that is the same as
For Ferrite cores
N=1000 x sqrt of (your desired L (in mH) / AsubL (mH/1000turns)

That needs verification, an error her could explain my misunderstanding.

I'm having a problem relating that to an inductor used in an oscillator.
From this article, > http://techlib.com/files/crvco.pdf

It says,
"the VCO coil, which uses seven turns of 30 gauge wire on a
Ferroxcube core (P/N: 135T050-4C4)"

P/N: 135T050-4C4 is a 1/2" toroid of 4C4 material.

The oscillator has a frequency range of 20MHz to 150MHz.
What I don't understand is 30 turns on a AsubL 75(nH) core
is 76.8 uH. I assume that is way to high for a 20MHz to 150MHz
oscillator.

What have I missed?

A couple of somewhat educated leaps of faith I have made are the
following. From 25 years ago, I know that 4C4 material was replaced with
4C6 material. And now searching data sheets I see 4C6 has been replaced
by 4C65. So I'm assuming a 1/2" toroid of 4C65 which the datasheet says
has AsubL if 75 (nH) is the same as a 1/2" core of 4C4.
If it helps, 4C4 and 4C65 both have an Initial Permeability of 125.

I have not been able to find any datasheet of the original 4C4 and any
catalogs I have with 4C4 do not include toroids.

Thanks, Mikek
 
amdx wrote...
What I don't understand is 30 turns on a AsubL
75(nH) core is 76.8 uH.
Click to expand...

No doubt the 30-turn spec is for a core with
a gap, which greatly reduces A_L. Ungapped
cores have very unstable A_L values.


--
Thanks,
- Win
 
amdx wrote:
I know and use the formulas for calculating turns on a core.
For Ferrite cores
N=1000 x sqrt of (your desired L (in mH) / AsubL (mH/1000turns)
For Iron Cores
N=100 x sqrt of (your desired L (in uH) / AsubL (uH/100)

Now I have a core that says AsubL is 75 (nH)
Assuming that is 75nH for one turn, that is the same as
For Ferrite cores
N=1000 x sqrt of (your desired L (in mH) / AsubL (mH/1000turns)

That needs verification, an error her could explain my misunderstanding.

I'm having a problem relating that to an inductor used in an oscillator.
From this article, > http://techlib.com/files/crvco.pdf

It says,
"the VCO coil, which uses seven turns of 30 gauge wire on a Ferroxcube
core (P/N: 135T050-4C4)"

P/N: 135T050-4C4 is a 1/2" toroid of 4C4 material.

The oscillator has a frequency range of 20MHz to 150MHz.
What I don't understand is 30 turns on a AsubL 75(nH) core
is 76.8 uH. I assume that is way to high for a 20MHz to 150MHz
oscillator.

What have I missed?
Click to expand...

Good grief, what a mess. Just memorize L = A_l N^2. Express
everything in SI base units and forget about all these factors
of 1000.

Seven (not 30!) turns on this core gives 75nH * 7^2 = 3.5uH.
That's still a lot for 150MHz, but probably manageable.

Jeroen Belleman
 
On 8/28/2019 9:30 AM, Winfield Hill wrote:
amdx wrote...

What I don't understand is 30 turns on a AsubL
75(nH) core is 76.8 uH.

No doubt the 30-turn spec is for a core with
a gap, which greatly reduces A_L. Ungapped
cores have very unstable A_L values.
Click to expand...
It's a toroid! No mention of any gap.
Mikek
 
On 28/08/2019 17:06, amdx wrote:
On 8/28/2019 9:30 AM, Winfield Hill wrote:
amdx wrote...

What I don't understand is 30 turns on a AsubL
75(nH) core is 76.8 uH.

  No doubt the 30-turn spec is for a core with
  a gap, which greatly reduces A_L.  Ungapped
  cores have very unstable A_L values.


 It's a toroid! No mention of any gap.
               Mikek
Click to expand...

Probably iron powder, the gap is distributed. The Al value is normally
pretty accurate on these 'gapped' low Al cores, so 30 turns should give
30*30* 75nH = 67.5uH which is a bit far out really. Maybe you misread
76.8uH as 67.8uH or you miscounted and wound 32 turns. 32*32*75nH =
76.8uH

Cheers
--
Clive
 
On 8/28/2019 10:19 AM, Jeroen Belleman wrote:
amdx wrote:
I know and use the formulas for calculating turns on a core.
For Ferrite cores
N=1000 x sqrt of (your desired L (in mH) / AsubL (mH/1000turns)
For Iron Cores
 N=100 x sqrt of (your desired L (in uH) / AsubL (uH/100)

 Now I have a core that says AsubL is 75 (nH)
Assuming that is 75nH for one turn, that is the same as
For Ferrite cores
N=1000 x sqrt of (your desired L (in mH) / AsubL (mH/1000turns)

That needs verification, an error her could explain my misunderstanding.

I'm having a problem relating that to an inductor used in an oscillator.
 From this article, > http://techlib.com/files/crvco.pdf

It says,
"the VCO coil, which uses seven turns of 30 gauge wire on a Ferroxcube
core (P/N: 135T050-4C4)"

P/N: 135T050-4C4 is a 1/2" toroid of 4C4 material.

 The oscillator has a frequency range of 20MHz to 150MHz.
What I don't understand is 30 turns on a AsubL 75(nH) core
is 76.8 uH. I assume that is way to high for a 20MHz to 150MHz
oscillator.

What have I missed?


Good grief, what a mess. Just memorize L = A_l N^2. Express
everything in SI base units and forget about all these factors
of 1000.
Click to expand...

Except most of the data books I have specify A_L in mH/1000 turns.
Yes, I could multiply the databook A_l in mH/1000 value my 100,000,000
and use L = A_l N^2. It works probably easier.


Seven (not 30!) turns on this core gives 75nH * 7^2 = 3.5uH.
That's still a lot for 150MHz, but probably manageable.
Click to expand...

Ah, that make a big difference although their cap is 3pf or 1.5pf
I don't know if the variable caps are series in the LC circuit.
Still 3.5uH and 1.5pf is... ya, never mind, they are adjusting L and C
so I'm not sure what values are.
7 turns instead of 30 solved my dilemma.
Also tells me I need a lot more turns for 100uh! (37 Turns)

Thank you for helping, Mikek


> Jeroen Belleman
 
On 8/28/2019 11:27 AM, Clive Arthur wrote:
On 28/08/2019 17:06, amdx wrote:
On 8/28/2019 9:30 AM, Winfield Hill wrote:
amdx wrote...

What I don't understand is 30 turns on a AsubL
75(nH) core is 76.8 uH.

  No doubt the 30-turn spec is for a core with
  a gap, which greatly reduces A_L.  Ungapped
  cores have very unstable A_L values.


  It's a toroid! No mention of any gap.
                Mikek

Probably iron powder, the gap is distributed.  The Al value is normally
pretty accurate on these 'gapped' low Al cores, so 30 turns should give
30*30*  75nH = 67.5uH which is a bit far out really.  Maybe you misread
76.8uH as 67.8uH or you miscounted and wound 32 turns.  32*32*75nH = 76.8uH

Cheers
Click to expand...

Ya, mixed up some other calcs in with this thought.

The article as pointed out by Jeroen said 7 turns not 30.
Mikek
 
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